1. Field of the Invention
The present invention relates in general to a gas spring, and more particularly to a gas spring which is applied to a hatch type door of a vehicle for keeping the door opened unless an external force to close the door is applied thereto.
2. Description of the Prior Art
In order to keep the hatch type door opened against the weight of the door itself, there has been proposed a telescopically movable gas spring which generally comprises a cylinder body pivotally connected to the vehicle body, a free-piston sealingly and slidably disposed in the cylinder body to divide it into a gas chamber and a liquid chamber, a main piston slidably disposed in the liquid chamber to divide it into first and second liquid chamber sections which are communicated with each other by only an orifice formed in the main piston, and a piston rod secured at its one end to the main piston and projecting axially from the cylinder body, the other end of the rod being pivotally connected to the door. When the door is under manual opening operation and the opening movement of its exceeds a predetermined degree, it is forced to open automatically against its own weight and keeps its full open position. This operation is achieved by a repelling force which is accumulated by the gas chamber when it is compressed upon closing of the door. Thus, in a cold season such as winter, there may occur a problem in that the gas volume in the gas chamber reduces considerably as compared with that in other seasons, thereby lowering the repelling force, so that the desirable operation of the gas spring is not achieved. In fact, it sometimes happens that the door closes spontaneously by its own weight after the door is manually opened to the fully open position.